Selective circuits



Dec. 9, 1 24. 1,518,495

' L. ESPENSCHIED SELECTIVE CI'RCUTTS Filed Sept. 26, 1919 3 Sheets-Sheet-1 g 2 l 2; 25 F E'fik;

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L. ESPENSCHIED SELECTIVE CIRCUITS Filed Sept. 26, 1919 3 Sheets-Sheet 2INVEN TQR. L. E8 4 emschbed A FAI 3 Sheets-Sheet 5 INVENTQR. L.ESensc/ued AT 0 EY L. ESPENSCHIED SELECTIVE CIRGUTTS.

Filed Sept. 26, 1919' Dec. 9, 1924- Patented Dec. 9, 1924,

UNITED STATES PATENTOFFICE.

LLOYD ESPENSCHIED, or nonLIs, NEW YORK, ASSIGITOR T AMERICAN 'rnnnrnonn[AND rnnrzemn coMrANY, A CORPORATION or new roan.

SELECTIVE CIRCUITS.

Application filed September 26, 1919. Serial NO. 326,521.

To all whom it may concern: Be it known that I, LL YD residing atHollis, in the county of Queens and State of New 'York,have inventedcertain Im rovements in SelectiveCircuits, of which t e followingis"a'spec'fication.

This invention relates to multiplex transmiss'ioncircuits and moreparticularly to arrangements whereby a plurality of Channels may beassociated w'th acommon transmission circuit without interferencebetween the channels. s v

One of the features of the invention resides in the provision of novelselective devices to prevent interference between the channels.

Another feature of the invention relates to a form of coupling devicefor coupling tuned selective circuits in such a manner as to obtainsharp selectivity and efficient transmission.

Another feature of the invention relates V to. the provision of meanswhereby a plural- -ity of channels may be serially related to a commontransmission circuit in such a manner that the two sides of thetransmission circuit will be balanced.

Other and further features of the inventiori will be clear from thefollowing description when read in connection with the accompanyingdrawing, Figures 1 to 4 of which illustrate a plurality of embodimentsof the invention.

'Referring to Figure 1, ML designates a transmission line over: which aplurality of transm'ssions may take place simultaneously. A commontransmitting circuit TL v and a common receiving circuit RL are .as-

sociated with the line ML through a balanced transformer arrangement 10and the line ML is balanced by an artifical line or network vMN, in"order to render the circuits TL and BL. substantially conjugate. Aplurality of transmitting channels T T etc. are bridged across thecommon transmit ting circu t TL, whereby a plurality of signals may besimultaneously impressed upon the line ML for transmission to a distantstation. In a similar manner a plurality of receiving1 channels, R Retc. are brdgecl across t e common. receiving circuit RL, whereby aplurality of signals simultaneo1rs1y transmitted over the line ML from aEsrnnscmnn,

may assume a wide variety of forms and for purposes of illustration adifferent form of selective device is shown associated with each of thechannels of Figure 1; For instance, the selective device asso'ciatedwith the channel It, may comprise a pair of resonant circuits F, and Floosely coupled through a transformer comprising w'ndmgs 11 and 12. Thewindings Hand 12 also serve as inductances which, in conjunction withcapacities 13 and 14, serve to tune the resonant circuits to a desiredfrequency.

Instead of us'ng the mutual inductances of the two windings of thetransformer for coupling the two resonant circuits, an autotransformerarrangement may be used, as shown in connection with the resonantcircuits F and F of the channel B In this case the circuits are tuned bymeans of condensers 15 and 16 and inductances 17 and 18, while a smallcoupling inductance 19 is shunted across the resonant circuits-F and Fat the junction points. The self-induc- 'prsing the windings 11 and 12of the channel R The arrangement associated with the channel It, issimilar to that associated with 3,, except that the tunin inductancesand ca acities are interchange thus the tuning in uctance 21 of theresonant circuit F is in shunt relation with respect to the channel,instead of in series, as in the case of inductance 18 of channel B Soalso the capacity 23 is in series instead of in shunt, with respect tothe channel R The coupling inductance 24 is in all respects simiiar tothe inductance 19.

Instead of an inductive coupling, 'a ca pacity coupling may be utilized,as illustrated in connection with the channel 8,. In this'case theresonant circuits F, and F, are meat means of inductances 25 and 26 andcapacit'es 27 and 28, these capacities being shunted acrossthe channeland being relatively large in value. For

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coupling purposes capacities 29 may be serially included in the channelbetween the resonant circu'ts and for loose coupling these capacitiesshould be relatively small in value.

If desired, a series-shunt coupling may be employed, as illustrated inconnection with the channel B In this case the resonant circuits F and Fare tuned by means of capacities and 31 and inductances 32 and 33,,while the two circuits are coupled by means of series capacit es 34 ofrelatively small value and shunt inductances 35 and 36 which are also ofrelatively small value.

Instead of shunt inductances of relatively small value, large shuntcapacities may be substituted, asindicated in connection w'th thechannel R in which the resonant cir- V cuits F and F are tuned by meansof capacities 37 and 38 and inductances 39 and 40. The coupling in thecase is obtained by means of small series capacities 41 and .ar e shuntcapacities 42 and 43.

nstead of a shunt inductive coupling havingself-inductance fortuning thecircuits and mutual inductance for coupling the circuits as shown inconnection with channel R a capacity arrangement having mutual capacityfor coupling the circuits and individual capacity for tuning thecircuits, may be substituted as illustratedin connection with thetransmittin channel T In this case the resonant circuits F. and F 5comprise tuning lnductances 44 and 45, while tuning capacity is obtainedfrom a condenser arrangement 46. This condenser arrangement comprises aplurality r the shunt inductive coupling associated with of plates,certain of which are individual I to the resonant circuits F and F andother plates which are common to both circuits. the capacity of thelatter plates serving as a'mutual coupling capacity.

i A shunt capacity coupling equivalent to the channel R is illustratedin connection and inductances 54 and 55. these elements I beinginterchanged with respect to the corresponding elements shown inconnection with the channel T The large shunt capacity 56 serves as acoupling element.

Instead of a series capacitative' coupling such as is illustrated inconnection with the channel R a series inductive coupling may be used,as shown in connection with the transmitting channel T In this instancethe resonant circuits F, and F. are tuned by means of inductances 57 and58 and shunt capacities 59 and 60. Relatively large inductance elements61 serially included in the sides of the channel between the resonantcircuits F and .Frl, serve as coupling'elements. I i

In a similar manner the series capacities 34-and 41 of the coublinaElements of the receiving channels R and H may be replaced by largeseries inductances 66 and 73, as illustrated in connection with thetransmitting channels T and T The small shunt inductances 67 and "68 ofthe channel T correspond to the similar inductances 35 and 36 of thechannel R while the large shunt capacities 74 and 75 of the couplingelement associated with the transmitting'channel '1 correspond to thesimilar capacities 42 and 43 of the receiving channel R 7 The severaltypes of coupling elements illustrated in connection with thetransmitting channels have a slight advantage over their prototypesillustrated inconnection with the receiving channels. in that they tendto reduce harmonics: for instance, the large shunt capacity of thecondensers 46, 51 and 56 associated with the channels T T5 and T providea shunt path for harmonies, of low impedance. So also the large seriesinductancesfil, 66 and 73 of the channels T T and T oiferrelativelylarge impedance to harmonics. thereby preventing the transmission ofsuch harmonics from one tunedcircuit to the. other.

In the arrangement shownin Figure 1, the channels R R etc: T T etc. areall in bridged relation with respect to the comnon transmissioncircuits-BL and TL. F igure 2 illustrates a modified arrangement inwhich the channels are associated mutually in series with respect to thecommon transmission circuits RL and TL. Thus the channel R is associatedwith the circuit RL by including the shunt tuning capacity'l3 of theresonant circuit F serially in the transmission circuit R.. In a similarmanner the receiving channel R is serially connected to the circuit BLby arranging the shunt tuning capacity 15 of the resonant circuit Ii inseries with the transmission circuit RL. In

comprise capacity elements 30 and 31, said and need not be described.

In some instances the series arrangement shown in Figure 2 may beundesirable by reason of unbalances to ground and the partialshort-circuiting of the terminal cir-i cuits. For instance, in the caseof the channels T, and T',, if a vacuum tube is included in thechannels, as illustrated in connection with the channel T then, with thefilaments of the tubes grounded, as indicated in connection -with thechannel T the terminal condenser 52 will be partially short-circuitedover a path extending from the lower terminal of 52 over the lower sideof tuuing in ductances 54 and 55 to the ground of the filaments andback" through the lower side of circuits F and F to the upper terminalof the condenser 52. Furthermore, the arrangement shown in Figure 2 isnon-symmetrical with regard to the two sides of'the transmissioncircuits RL and TL, since the series connection of the channels areincluded in one side only of the common circuits, thereby tending tounbalance the two sides of the circuits. These objections may beovercome by means of the arrangement illustrated in Figure 3, in

which the channels are inductively associated with the common circuitsRL and TL. The inductive connection permits of serially relating thechannels to the common circuit and at the same time preventsshortcircuiting of the terminal circuit in the manner above described.By arranging the inductive connections so that half of the inductancethereof is inclined ineach side of the common transmission circuits RLand TL, unbalancing of said circuits will be prevented.

For example, the channel B, may terminate in a transformer 76,comprising three windings, one of which is serially included in thechannel R the other windings being serially included, onein each side ofthe circuit FL. The channelR, may be coupled in a similar manner'bymeansof a transformer 77. In the case of the channel R since the resonantcircuit F,v of Figure 2 terminates in a: shunt inductance 20, thecorresponding channel R of Figure 3 may be associated with the circuitRL through a three-winding transformer 78, which not only serves as ameans for assoresonant circuit F The same considerations apply to thetransformer 79, which may be used for coupling the channel R, with thecircuit BL. In the case of'channels R and R since the resonant circuitsF5 and F terminate in shunt condensers,

the channels must be terminated in transformers 80 and 81, for thepurpose of asso- T are associated with the common circuit TL. through'special transformers '84, 86 and 87. i

A similar arrangement is illustrated in Figure 4, in which, instead ofemploying tuned circuits for frequency separation, broad band filtersare used. These filters are preferably of the type illustrated in theUnited States patents to George A. Campbell, Nos: 1,227,113 and1,227,114, dated May 22, 1917, and are designed to transmit bands offrequencies of suificient width to allow for the transmission ofsignaling frequencies which extend over a considerable range, as is thecase in the transmission of telephone currents. t

In Figure 4 transmitting channels T to T, inclusive, include broadband'filters BF BF,, BF and BF respectively, while the I correspondingreceiving channels R, to R, inclusive, include broad band filters B,F,,B,F,, B,F and B F respectively. The channels T, to T inclusive, areassociated with the common transmitting circuit TL throughtransformerslOl, 102, 103 and 104, each of which is balanced by means ofwindings included in each side of the circuit TL. In a similar mannerthe receiving channels R, to R, inclusive, are associated with thecommon receiving circuit RL through balanced transformers 111, 112, 113and 114, of similar construction. By means of this arrangement the,channels are mutually arranged in series with respect to the commontransmission circuit, while maintaining'the two sides of the commoncircuit balanced.

It will be obvious that the general principles herein disclosed may beembodied ferent from those illustrated," without (19- parting from thespirit of the invention as defined in the following claims.

What is claimed is: '1. A selective device comprising a pair ofselective circuits, each circuit including inductance and capacitywhereby the circuits may be tuned to the same desired frequency,

and means for loosely coupling the tuned circuits, comprising series andshunt impedance elements, one of which is inductive and the other ofwhich is capacitative, and said'impedance elements being so proportionedand related with respect to each other and with respect to said tunedcircuits as to roduce a greater discrimination against requencies ononeside of the frequency to which the selective circuits are tuned thanthat due to the selectivity of the tuned circuits themselves.

2. A selective device comprising a pair of selective circuits, eachcircuit including inductance andcapacitywhereby the circuits ma be tunedto'the same desired frequency, meansfor loosely coupling the tunedcircuits, comprising series and shunt impedance elements one of which isinductive, and said impedance elements being so proportioned and'relatedwith respect to each;

other and with'respect to said tuned circuits as to produce a greaterdiscrimination against frequencies on'one side' of the frequency towhich the selective circuits are tuned than that due to the selectivityof the tuned circuits themselves.

3. A selective device comprising a pair of circuits, each includinginductance and capacity whereby the circuits may be tuned to the samedesired frequency, and means for loosely coupling the circuits,comprising impedance elements of two types, one type being indiyidualrtosaid circuits and the other type common to said circuits, one of saidtypes of impedance elements being inductive and the other type beingcapacitative, and said impedance elements being so proportioned andrelated with respect to each other and with respect to said tunedcircuits as to produce a greater. discrimination against frequencieson-one side of the frequency to which the selective circuits are tunedthan that due to the selectivity of the tuned circuits themselves.

' 4. A selective device comprising a pair of tuned circuits,each'including inductance and capacity whereby the circuits may be tunedto the samedesired frequency, and means for looselycoupling thecircuits, comprising impedance elements individual to said circuits andimpedance elements common to said circuits one of said impedanceelements being inductive, and said impedance elements being soproportionedand related with respect to each other and with respect tosaid tuned circuits as to produce a greater discrimination againstfrequencies on one side of the frequency to which the" selectivecircuits are tuned than that due to the selectivity of the tunedcircuits themthe same desired frequency, and meansfor loosely coupllngsaidcircuits, includin im- 1 pedance elements of two types, one 0 saidtypes being shunted across said circuits and impedance elements of theother type serially connecting said circuits, one of said types ofimpedance elements being inductive and the other type beingcapacitative, andsaid impedance elements being so proportioned andrelated with respect to each other and with respect to said tunedcircuits as to produce a greater discrimination against frequencies onone 1 side of the frequency'to which the selective circuits aretunedthan that due to the selectivity of the'tuned cir-' cuits themselves.

6. A selective device comprising'apair of selective circuits, eachincluding inductance and capacity whereby they may be tuned to the samedesired frequency, and means for loosely coupling said circuits,including impedance elements shunted across said circuits and impedanceelements serially connecting said circuits one of said impedanceelements being inductive, and said and related with respect to eachother and withrespect to said tunedcircuits as to produce a greaterdiscrimination against frequencies on one side ofthe frequency toinductive reactance, and said. impedance elements being so proportionedand related with respect to each other and with respect to saidtunedcircuits as to produce a greater discrimination against frequencieson one side of the frequency to which the selective circuits aretunedthamthat due to the selectivity of the tuned circuits themselves.

8. A selective device comprising a pair of selective circuits,each'including inductance and capacity whereby said circuits may betuned to the samedesired frequency,

and means for loosely coupling said circuits, comprising an impedancein'shunt relation with respect to said circuit, and an impedance inseries relation with respect to said circuit, one of said impedanceshaving an inductive reactance, and said impedance elements being soproportioned and related with respect to each other and with respect tosaid tuned circuits as to produce a greater discrimination againstfreimpedance elements being so proportioned quencies on one side of thefrequency to which the selective circuits are tuned than that due to theselectivity of the tuned circuits themselves.

9. In a multiplex transmission'system, a transmission circuit, aplurality of signaling channels associated with said circuit at one endthereof and adapted for transmission in the same direction, selectivedevices in each signaling channel and series conne tions between eachchannel and said transmission circuit, said series connections beingbalanced with respect to the two sides of the transmission circuit.

10. In a multiplex transmission system, a transmission circuit, aplurality of channels associated with said transmission circuit at oneend thereof and adapted for transmission in the same direction,selective means in each channel and means in each channel forassociating each channel with said transmission circuit, comprising atransformer having balanced windings in each side of the transmissioncircuit.

11. In a multiplex transmission system, a transmission circuit, aplurality of channels associated with said circuit one end thereof andadapted for transmis ion in the same direction, selective devices ineach channel, and means for in efiect serially relating each channel tothe transmission circuit, said means comprising transformers, eachtransformer having windings in each side of the transmission circuit anda winding in the corresponding channel.

In testimony whereof, I have signed my name to this specification thisth day of September, 1919.

LLOYD ESPENjSCHIED.

